氧化还原可逆Nb2TiO7复合阴极电解池高温水蒸气电解研究

系统地研究Nb₂TiO₇与Nb_1.33Ti_0.67O₄材料相互转变的氧化还原循环可逆性能,同时研究Nb2TiO7和Nb_1.33Ti_0.67O₄样品随温度和氧分压变化的电导率,并与复合电极对称电池和电解池的电化学性能相关联. 在830 oC下,对Nb_1.33Ti_0.67O₄复合电极电解池进行水蒸气的电解研究测试. 电流电压曲线和电解池短期性能测试表明在低电压下主要为电极的还原和活化过程;而在高电压下主要为水蒸气的电解. 当3%H₂O/Ar/4%H_{2气体通入阴极时电解池水蒸气电解的法拉第效率为98.9%;而当通入气体转换为3%H2O/Ar时效率为89%.}     

钙钛矿型中温固体氧化物燃料电池阴极Ba0.5Sr0.5Al0.1Fe0.9O3-δ

研究一种新型不含钴的钙钛矿型中温固体氧化物燃料电池阴极Ba_0.5Sr_0.5Al_0.1Fe_0.9O_3-δ (BSAF)材料的晶体结构、电导率以及在对称电池中的电极极化性能. 研究发现,BSAF阴极在空气中低于450 oC表现出典型的具有正温度系数的半导体行为,最高电导率达到14 S/cm;在450-750 oC,却表现出负温度系数,且电导率在750 oC下降到6 S/cm. 电化学研究表明,在基于混合离子导体的对称电池中,BSAF阴极在650-700 oC表现出良好的电极极化性能.以3%H₂O/H₂为燃料和空气为氧化剂,单电池在700 oC的开路电压和最大功率输出分别达到420 mW/cm².     

钙钛矿型氧离子导体KNb1-xMgxO3-δ的制备和表征

在高温高压 ( 4 0GPa ,870℃ )下合成了具有正交钙钛矿结构的KNb1 -xMgxO3-δ(x =0 0— 0 3 )系列固体电解质 ,并系统地研究了Mg掺杂对其结构相变和导电性的影响 .变温拉曼谱和DTA测量结果表明 ,随着温度的升高 ,KNb1 -xMgxO3-δ发生了结构相变 ,由铁电正交、四方相转变为顺电立方相 .由于Mg掺杂削弱了B位离子对自发极化的贡献以及A位离子与BO6 八面体间的耦合作用导致了居里温度下降 .其中KNb0 85Mg0 1 5O2 775的居里点大约下降 40℃ ,为 3 92℃ .阻抗谱测量表明 ,所有样品都具有离子导电特征 ,但晶界效应较强 ,电导主要由晶界决定 .通过掺杂 ,提高了样品的电导率 ,其中KNb0 9Mg0 1 O2 85的氧离子电导率最高 ,70 0℃时达到 1.2× 10 - 3S cm .     

KNb1-xTixO3-δ固溶体的合成与表征

利用高温高压法首次合成了KNb1-xTixO3-δ(x=0～0.4)系列固溶体,并使用X射线衍射、TG-DTA、Raman谱和交流阻抗谱等对样品的结构、热稳定性和导电性进行了表征.XRD结果表明,随掺杂量的增加,晶胞体积减小;Ti掺杂引起了固溶体结构的转变,x<0.15的样品为正交钙钛矿结构,而x≥0.15的样品几乎为纯四方相结构.Raman谱和DTA结果显示,Ti掺杂使四方相区宽化,并且随掺杂量的增加,相变温度逐渐下降.阻抗谱测量表明,所有样品均以离子导电为主,其中KNb0.85Ti0.15O2.925的氧离子导电率最高,在800 ℃时达到5.6×10-3 S*cm-1,在测量温度范围内,电导率可以拟合成两条直线,低温活化能小于高温活化能.     

钙钛矿型氧离子导体KNb1-xMgxO3-δ的制备和表征

在高温高压（4.0GPa，870℃）下合成了具有正交钙钛矿结构的KNb_1-xMg_x O_3-δ（x=0.0—0.3）系列固体电解质，并系统地研究了Mg掺杂对其结构相变和导电性的影响.变温拉曼谱和DTA测量结果表明，随着温度的升高，KNb_{1-xMgxO3-δ发生了结构相变，由铁电正交、四方相转变为顺 电立方相.由于Mg掺杂削弱了B位离子对自发极化的贡献以及A位离子与BO关键词： 钙钛矿 离子电导 1-xMgxO3-δ')" href="#">KNb1-xMgxO3-δ 高温高压 铁电相变}     

Efficient Thickness of Solid Oxide Fuel Cell Composite Electrode

利用一个物理模型计算了固体氧化物燃料电池复合电极的有效厚度. 此模型考虑了复合电极内部的电化学反应,电子和离子的传递,以及电极的微结构. 电极的有效厚度对应于电极性能最优时电极的理论厚度,经过模型计算表明此厚度同时为电荷转移电阻率、有效离子(电子)电阻率以及单位体积内三相线长度的函数. 通过与实验数据比较验证了模型的可用性. 通过模拟表明电极成分、粒子大小、电极材料的本征电阻率、不同的操作温度以及电极反应的机理都影响着复合电极的有效厚度.     

Effects of novel benzotriazole based zwitterionic salt as electrolyte additive for lithium ion batteries

A novel zwitterionic lithium-benzotriazole sulfobetaine is fabricated by grafting 1,3– propanesultone onto benzotriazole and then lithiating it. The resultant lithium-benzotriazole-sulfobetaine additive is used as an electrolyte additive in lithium ion batteries in 1 M LiPF₆ (ethylene carbonate/dimethyl carbonate = 1:1). The electrolytes with the lithium-benzotriazole sulfobetaine shows higher ionic conductivities (2.18 $\times$ 10⁻² S cm⁻¹) compared to the bare electrolyte (1.07 $\times$ 10⁻² S cm⁻¹) and greater electrochemical stability (anodic limit at ~5.5 V vs. Li/Li⁺) than the pure electrolyte (anodic limit at ~4.6 V vs. Li/Li⁺). The discharge capacity of the lithium cobalt oxide/graphite cells is improved at higher C-rates with the addition of lithium-benzotriazole sulfobetaine due to increased ionic conductivity. The lithium cobalt oxide/graphite cells with the lithium-benzotriazole sulfobetaine additive also show stable cycling performance. These findings warrant the use of lithium-benzotriazole sulfobetaine as an electrolyte additive in lithium ion batteries.     

Polymer electrolytes based on ethylene oxide–epichlorohydrin copolymers

In this work we studied the ionic conductivity for three copolymers of the title co-monomers as a function of LiClO₄ content, temperature and ambient relative humidity. We also investigated the interactions between the salt and the co-monomer blocks in the copolymers and its effect on the morphology and thermal properties of the copolymer/salt complexes. Our data indicate that the Li⁺ ion predominantly interacts with the ethylene oxide repeating units of the copolymers. The copolymer with the highest ionic conductivity was obtained with an ethylene oxide/epichlorohydrin ratio of 84/16 containing 5.5% (w/w) of LiClO₄. It showed a conductivity of 4.1×10⁻⁵ S cm⁻¹ (30°C, humidity< 1 ppm) and 2.6×10⁻⁴ S cm⁻¹ at 84% relative humidity (24°C). The potential stability window of the copolymer/salt complex is 4.0 V, as measured by cyclic voltammetry. For comparison, we also prepared a blend of the corresponding homopolymers containing LiClO₄; it showed higher crystallinity and lower ionic conductivity.     

Effects of plasticizer and nanofiller on the dielectric dispersion and relaxation behaviour of polymer blend based solid polymer electrolytes

Solid polymer electrolytes consisted of poly(ethylene oxide) (PEO) and poly(methyl methacrylate) (PMMA) blend (50:50 wt/wt%) with lithium triflate (LiCF₃SO₃) as a dopant ionic salt at stoichiometric ratio [EO + (CO)]:Li⁺ = 9:1, poly(ethylene glycol) (PEG) as plasticizer (10 wt%) and montmorillonite (MMT) clay as nanofiller (3 wt%) have been prepared by solution cast followed by melt–pressing method. The X–ray diffraction study infers that the (PEO–PMMA)–LiCF₃SO₃ electrolyte is predominantly amorphous, but (PEO–PMMA)–LiCF₃SO₃–10 wt% PEG electrolyte has some PEO crystalline cluster, whereas (PEO–PMMA)–LiCF₃SO₃–10 wt% PEG–3 wt% MMT electrolyte is an amorphous with intercalated and exfoliated MMT structures. The complex dielectric function, ac electrical conductivity, electric modulus and impedance spectra of these electrolytes have been investigated over the frequency range 20 Hz to 1 MHz. These spectra have been analysed in terms of the contribution of electrode polarization phenomenon in the low frequency region and the dynamics of cations coordinated polymer chain segments in the high frequency region, and also their variation on the addition of PEG and MMT in the electrolytes. The temperature dependent dc ionic conductivity, dielectric relaxation time and dielectric strength of the plasticized nanocomposite electrolyte obey the Arrhenius behaviour. The mechanism of ions transportation and the dependence of ionic conductivity on the segmental motion of polymer chain, dielectric strength, and amorphicity of these electrolytes have been explored. The room temperature ionic conductivity values of the electrolytes are found ∼10⁻⁵ S cm⁻¹, confirming their use in preparation of all-solid-state ion conducting devices.     

Co-electrolysis of CO2 and H2O in solid oxide cells: Performance and durability

This study examines the initial performance and durability of a solid oxide cell applied for co-electrolysis of CO₂ and H₂O. Such a cell, when powered by renewable/nuclear energy, could be used to recycle CO₂ into sustainable hydrocarbon fuels. Polarization curves and electrochemical impedance spectroscopy were employed to characterize the initial performance and to break down the cell resistance into the resistance for the specific processes occurring during operation. Transformation of the impedance data to the distribution of relaxation times (DRT) and comparison of measurements taken under systematically varied test conditions enabled clear visual identification of five electrode processes that contribute to the cell resistance. The processes could be assigned to each electrode and to gas concentration effects by examining their dependence on gas composition changes and temperature.This study also introduces the use of the DRT to study cell degradation without relying on a model. The durability was tested at consecutively higher current densities (and corresponding overpotentials). By analyzing the impedance spectra before and after each segment, it was found that at low current density operation (− 0.25 A/cm² segment) degradation at the Ni/YSZ electrode was dominant, whereas at higher current densities (− 0.5 A/cm² and − 1.0 A/cm²), the Ni/YSZ electrode continued to degrade but the serial resistance and degradation at the LSM/YSZ electrode began to also play a major role in the total loss in cell performance. This suggests different degradation mechanisms for high and low current density operation.     

Ionic conductivity of electrolytes based on star-branched poly(ethylene oxide) with high concentration of lithium salts

Electrolytes based on star-branched poly(ethylene oxide) with lithium bis(trifluoromethanesulfone)imide LiTFSI and lithium iodide salts were prepared by casting from solution. The electrical properties of electrolytes subjected to various heating and cooling runs were studied by impedance spectroscopy and impedance spectroscopy simultaneous with optical microscope observation. Differential scanning calorimetry was used for additional characterization. The results indicate that in electrolytes with high content of salt, values of ionic conductivity comparable to that of dilute electrolytes can be achieved. Moreover, electrolytes with high amount of salt seem to show weaker temperature dependence of conductivity. Promising results in terms of ionic conductivity were obtained for mixture of LiTFSI and lithium iodide. A few problems which may decrease the performance of studied system as a solid electrolyte were also identified, from which changes of physical properties of samples subjected to thermal cycles and aging seem to be the most important ones.     

Effects of cobalt metal addition on sintering and ionic conductivity of Sm(Y)-doped ceria solid electrolyte for SOFC

The effects of cobalt addition (0.5 and 1 wt.%) on densification and ionic conductivity of Ce_0.9Sm_0.1O_1.95 (10SDC) and Ce_0.9Sm_0.075Y_0.025O_1.95 (2.5Y-SDC) have been studied. X-ray diffraction (XRD) showed that Co had changed to Co₃O₄ and Co₃O₄ + CoO after firing at 900 °C and 1300 °C respectively. The addition of Co promoted densification to occur at lower temperatures with a more uniform grain growth and greatly improved both grain boundary and bulk conductivity for 10SDC. Significant improvement of grain boundary for the 2.5Y-SDC samples was obtained, even at 1300 °C sintering, while bulk conductivity was slightly improved. Rapid grain growth along with improvement of ionic conductivity was observed when the samples were sintered further at higher temperature. Superior ionic conductivity of the 2.5Y-SDC samples with Co addition to that of the bare 10SDC suggested the potential use of Co as the co-dopant in this system to reduce the content of costly rare earth usage.     

Influence of colloidal templates on the impedance spectroscopic behaviour of Pr0.7Sr0.3Fe0.8Ni0.2O3 for solid oxide fuel cell applications

The creation of porous materials with three-dimensional periodicity has been identified as being of potential interest for increasing the overall performance of solid oxide fuel cells (SOFC). In this work, we have investigated the formation of pore systems in the nanometer scale by replicating colloidal templates. Templating methods have been used to prepare iron-nickel-based perovskite Pr_0.7Sr_0.3Fe_0.8Ni_0.2O₃ material with nanoporous microstructure. Polymethyl methacrylate (PMMA), polystyrene (PS) and polycarboxylate (PC) microspheres with different diameters were used as pore formers. These samples were synthesized and characterized by thermogravimetric analysis, inductively coupled plasma atomic emission spectroscopy (ICP-AES), X-ray diffraction, transmission electron microscopy and field emission scanning electron microscopy. The polarization resistance of the materials was studied by Electrochemical Impedance Spectroscopy. The study demonstrated that templated porosity is maintained and highly influences on the impedance spectroscopic behaviour, being the material synthesized with policarboxylate microspheres the most interesting of the three used templates for SOFC applications.     

Li mobility in Li0.5 − xNaxLa0.5TiO3 perovskites (0 ≤ x ≤ 0.5): Influence of structural and compositional parameters

The dependence of Li mobility on structure and composition of Li_0.5 − xNa_xLa_0.5TiO₃ perovskites (0 ≤ x ≤  0.5) has been investigated by means of neutron diffraction, nuclear magnetic resonance and impedance spectroscopy. At 300 K, all samples display a rhombohedral superstructure (R-3c S.G.), where octahedra are out of phase tilted along [111] direction of the ideal cubic cell. The elimination of the octahedral tilting is responsible for the rhombohedral–cubic transformation, detected near 1000 K. In these perovskites, La and Na cations are randomly distributed in A sites, but Li ions are fourfold coordinated at unit cell faces of the cubic perovskite. Lithium conductivity, σ_300 K, decreases with the sodium content, decreasing from values typical of fast ionic conductors, 10^− 3 S/cm, to those of good insulators, 10^− 10 S/cm, when the interconnectivity between vacant A sites is lost (x > 0.3). In samples with x < 0.3, dc conductivity displays a non-Arrhenius behaviour, decreasing activation energy from ~ 0.37 to 0.25 eV when the sample is heated between 77 and 500 K. The temperature dependence of B_Li factors shows the existence of two regimes for Li motion. Below 373 K, Li ions remain partially located near square oxygen windows that connect contiguous A sites, but above 400 K, extended Li motions become dominant. The additional decrease of activation energy from 0.25 to 0.16 eV (low-temperature ⁷Li NMR value), should require the full elimination of octahedral tilting which is only produced above 1000 °C.